Characterization of mouse model-derived osteosarcoma (OS) cells in vitro and in vivo

Loss of RanGAP1 drives chromosome instability and rapid tumorigenesis of osteosarcoma

Chromothripsis is a catastrophic event of chromosomal instability that involves intensive fragmentation and rearrangements within localized chromosomal regions. However, its cause remains unclear. Here, we show that reduction and inactivation of Ran GTPase-activating protein 1 (RanGAP1) commonly occur in human osteosarcoma, which is associated with a high rate of chromothripsis. In rapidly expanding mouse osteoprogenitors, RanGAP1 deficiency causes chromothripsis in chr1q, instant inactivation of Rb1 and degradation of p53, consequent failure in DNA damage repair, and ultrafast osteosarcoma tumorigenesis. During mitosis, RanGAP1 anchors to the kinetochore, where it recruits PP1-γ to counteract the activity of the spindle-assembly checkpoint (SAC) and prevents TOP2A degradation, thus safeguarding chromatid decatenation. Loss of RanGAP1 causes SAC hyperactivation and chromatid decatenation failure. These findings demonstrate that RanGAP1 maintains mitotic chromosome integrity and that RanGAP1 loss drives tumorigenesis through its direct effects on SAC and decatenation and secondary effects on DNA damage surveillance.

MicroRNA-182 downregulates Wnt/β-catenin signaling, inhibits proliferation, and promotes apoptosis in human osteosarcoma cells by targeting HOXA9

We investigated the mechanisms by which microRNA (miR)-182 promotes apoptosis and inhibits proliferation in human osteosarcoma (OS) cells. Levels of miR-182 and Homeobox A9 (HOXA9) expression were compared between human OS and normal cells. Subjects were divided into OS and normal groups. We analyzed the target relationship of miR-182 and Homeobox A9 (HOXA9). Cells were then assigned into blank, negative control, miR-182 mimics, miR-182 inhibitors, siRNA-HOXA9, or and miR-182 inhibitors + siRNA-HOXA9 groups. Cell function was assayed by CCK-8, flow cytometry and wound healing assay. Additionally, we analyzed OS tumor growth in a xenograft mouse model. Dual-luciferase reporter assays indicated miR-182 directly targets HOXA9. Reverse transcription quantitative PCR and western blotting revealed elevated expression of miR-182, WIF-1, BIM, and Bax, and reduced expression of HOXA9, Wnt, β-catenin, Survivin, Cyclin D1, c-Myc, Mcl-1, Bcl-xL, and Snail in osteosarcoma cells treated with miR-182 mimic or siRNA-HOXA9 as compared to controls. Osteosarcoma cells also exhibited decreased cell proliferation, migration, and tumor growth, and increased apoptosis when treated with miR-182 mimic or siRNA-HOXA9. Correspondingly, in a xenograft mouse model, osteosarcoma tumor volume and growth were increased when cells were treated with miR-182 inhibitor and decreased by miR-182 mimic or siRNA-HOXA9. These results indicate that miR-182 downregulates Wnt/β-catenin signaling, inhibits cell proliferation, and promotes apoptosis in osteosarcoma cells by suppressing HOXA9 expression.

WWOX and p53 Dysregulation Synergize to Drive the Development of Osteosarcoma

Osteosarcoma is a highly metastatic form of bone cancer in adolescents and young adults that is resistant to existing treatments. Development of an effective therapy has been hindered by very limited understanding of the mechanisms of osteosarcomagenesis. Here, we used genetically engineered mice to investigate the effects of deleting the tumor suppressor Wwox selectively in either osteoblast progenitors or mature osteoblasts. Mice with conditional deletion of Wwox in preosteoblasts (Wwox^Δosx1) displayed a severe inhibition of osteogenesis accompanied by p53 upregulation, effects that were not observed in mice lacking Wwox in mature osteoblasts. Deletion of p53 in Wwox^Δosx1 mice rescued the osteogenic defect. In addition, the Wwox;p53^Δosx1 double knockout mice developed poorly differentiated osteosarcomas that resemble human osteosarcoma in histology, location, metastatic behavior, and gene expression. Strikingly, the development of osteosarcomas in these mice was greatly accelerated compared with mice lacking p53 only. In contrast, combined WWOX and p53 inactivation in mature osteoblasts did not accelerate osteosarcomagenesis compared with p53 inactivation alone. These findings provide evidence that a WWOX-p53 network regulates normal bone formation and that disruption of this network in osteoprogenitors results in accelerated osteosarcoma. The Wwox;p53^Δosx1 double knockout establishes a new osteosarcoma model with significant advancement over existing models. Cancer Res; 76(20); 6107-17. ©2016 AACR.